1. Field of the Invention
The present invention relates to a power amplifier for reducing non-linear distortion.
2. Description of the Related Background Art
In a single ended push-pull (SEPP) circuit, since the V.sub.BE -I.sub.C characteristic presents an exponential change, if this type of circuit is used as a power amplifier, distortion may occur. Conventionally, a voltage gain at a previous stage has been utilized to perform negative feedback (NFB) to remove such distortion, thereby improving the distortion ratio.
However, if a load impedance cannot be specifically known as in the case of an audio amplifier, performing NFB from an output may result in difficulties in ensuring the stability of a NFB loop system.
Thus, for providing a power amplifier which presents a low distortion ratio without NFB from an output, there is an amplifier which reduces distortion at a previous stage. An amplifier suitable for use in such a previous stage may be such one that is disclosed in Japanese Patent publication No. 61-41293. In this amplifier, as shown in FIG. 1, a PNP transistor Q.sub.1 having the base applied with an input signal is operated as an emitter follower, and the output signal from the emitter follower is used as an input to the base of an NPN transistor Q.sub.2. Then, these transistors Q.sub.1, Q.sub.2 in conductive types reverse to each other are supplied with currents i.sub.1 and i.sub.2, always in a fixed ratio relationship, by a current mirror circuit formed by transistors Q.sub.3, Q.sub.4, and resistors R.sub.2, R.sub.3. Incidentally, an emitter resistor R.sub.1 is arranged between the emitter of the transistor Q.sub.2 and the ground to define a circuit current. Also, a transistor Q.sub.5 is provided to obtain an output of this circuit, and has the base commonly connected with the base of the transistor Q.sub.3 to form a current mirror circuit. The current mirror circuit applies the resistor R.sub.5 with a current output which maintains a fixed ratio to a current flowing through the transistor Q.sub.2. An output transistor is further connected to the output of the amplifier to constitute a power amplifier. When the amplifier is used as an audio amplifier, the output stage is generally formed by a complementary SEPP.
However, in order to supply a load with a stable current from the output of the previous stage, the conventional power amplifier as described above requires an output stage such as an emitter follower to be connected thereto such that its output current is supplied to the load, which results in a problem that the number of elements constituting the power amplifier is increased and hence the circuit arrangement becomes complicated. Also, the distortion generated by transistors in the output stage has still been a problem.